In a conventional circuit network based on semiconductor device technology, functional devices made of semiconductors or insulators are connected together by relatively large metal traces designed to carry electrical signals. These structures typically require real estate on the order of tens of square micrometers, and more.
Mesoscopic structures are smaller, but still require significant real estate. To fabricate such a circuit network on a silicon substrate, diodes or transistors based on p-n junctions, or resistors made of doped semiconductors are connected by several ten nanometer wide metal lines deposited on the substrate, power is fed from a battery or an external generator, and a large ground plane is made by deposition of metal on the substrate which may be connected to the main ground. The resulting structure quickly becomes complicated and can typically require real estate on the order of hundreds of square nanometers, and more.
If the circuit network together with device elements is simply scaled down, the physical operation principle for these macroscopic devices undergoes a drastic change even at nanoscale, where the wave nature of the electrons play an important role in device operation. To further miniaturize the structures, a new device principle must be developed, adopting the atomic nature of constituent atoms forming the device.